An optical scanning apparatus that vibrates the distal end of a fiber, which optically guides light emitted from a light source, to make the output light from the fiber scan an observation target such that the pattern of the output light forms a spiral shape, thus performing a so-called spiral scan, has been proposed.
In such an optical scanning apparatus, the proximal end of the fiber is supported, whereas the distal end serving as a light output end is vibrated by being driven in two axial (x and y) directions that are orthogonal to the optical axis of the fiber and that are also orthogonal to each other. In this case, the phases in the two axial directions are shifted from each other by 90°, and the spiral scan is achieved by vibrating the distal end two-dimensionally in accordance with the same drive frequency while modulating and amplifying the amplitude of the vibration.
For example, PTL 1 discloses a technique in which a horizontal sine wave vibration drive signal and a vertical sine wave vibration drive signal whose phase is shifted by 90° from the horizontal signal are synchronized with each other and are amplitude-modulated in accordance with a triangular pattern so that a spiral scan pattern is formed.
PTL 2 discloses a technique for adjusting drive parameters, such as the amplitude of an applied voltage, the phase difference, and the drive frequency, while analyzing a spiral scan pattern acquired by an optical position detector (PSD) so that the scan pattern forms a perfect circle. In particular, the drive frequency is set close to the resonance frequency of the distal end of the fiber so that the maximum fiber amplitude can be obtained.